JavaScript/Arrays/Exercises

Topic: Arrays

1. What is the output of the following script?

"use strict";

const x = [];
x[1] = 5;
console.log(x);

x[2] = [, , 42];
console.log(x);

Click to see solution

[undefined, 5]
[undefined, 5, [undefined, undefined, 42]]

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2. Add elements

• Create an array with all odd numbers that are smaller than 10.
• Show the array with the alert command.
• Show how many elements the array contains.
• Add 2, 4, 6, 8 to the end of the array and show it again.
• Insert the value 20 on the 20th array element and show the array again.

Click to see solution

"use strict";

// literal notation
const arr = [1, 3, 5, 7, 9];
alert(arr);  // or: console.log(arr);

alert("The array contains " + arr.length + " elements.");

// add elements
arr.push(2, 4, 6, 8);
alert(arr);

// one certain element
arr[19] = 20;    // 19!
alert(arr);
alert("The array now contains " + arr.length + " elements.");

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3. Remove elements

• Create an array with all numbers from 1 to 6.
• Show the array with the alert command.
• Delete the first and last element and show the resulting array.

Click to see solution

"use strict";
const arr = [1, 2, 3, 4, 5, 6];
alert(arr);  // or: console.log(arr);

// remove elements
const first = arr.shift();
alert("Removed the first element: " + first);
alert(arr);

const last = arr.pop();
alert("Removed the last element: " + last);
alert(arr);

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4. Combine elements

• Create an empty array.
• Add 0, 1, 2 to the array with the push method and show the array.
• Create the string "0 + 1 + 2" out of the array using the join method and show the string.

Click to see solution

"use strict";

const arr = [];
arr.push(0);
arr.push(1);
arr.push(2);
alert(arr);

const str = arr.join(" + ");
alert(str);